Embodiments described herein relate to exhaust systems. More particularly, embodiments described herein relate to mounts for mounting components in an exhaust system.
An exhaust system associated with an engine includes an exhaust gas passageway for emitting the exhaust gases from the engine to the ambient. In the direction of flow of the exhaust gases on the exhaust gas passageway, the exhaust system may have a hydrocarbon doser, a pre-diesel oxidation catalyst (PDOC), a diesel oxidation catalyst/diesel particulate filter (DOC/DPF), a catalyst, an exhaust gas recirculation (EGR) cooler, and may include other components, or components in varying locations on the exhaust gas passageway. Some of these components are mounted in an exhaust pipe, and as a result, may be mounted in a way to permit the thermal expansion of the components within the exhaust pipe. Further, the components are susceptible to vibration and resonance through contact with the exhaust pipe.
Oscillating objects have a natural frequency, which is the frequency that the oscillating object tends to settle into if the object is not disturbed. The phenomenon in which a relatively small, repeatedly applied force causes the amplitude of an oscillating system to become very large is called resonance.
Exhaust systems have a natural frequency at which the exhaust system tends to vibrate. This natural frequency can be attributed to the physical shape and dimension of the exhaust system. The natural frequency of an exhaust system is primarily dictated by its length, which is functional in nature and cannot be altered substantially.
During on road operation of a vehicle, the exhaust system receives vibration pulses; for example, from engine combustion and road irregularities which substantially increase the rate at which the exhaust system is vibrating. Furthermore, the incoming vibration pulses received by an exhaust system can be at or near the natural frequency of the exhaust system, which causes the exhaust system to approach and sometimes reach resonance. The exhaust system reaching resonance can result in the destruction of the exhaust system.
The force that causes vibrations or oscillation to stop is called damping. If the proper damping mechanism is utilized, reaching resonance can be avoided. The most common damping mechanism used with exhaust systems is the incorporation of thermal blankets wrapped around the components. Other past efforts to increase the longevity of the exhaust systems have been directed to increasing the stiffness of the system sufficiently to reduce vibrations to within acceptable amplitudes.